1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for performing a handover of a wireless call, and specifically to performing a handover of a wireless call between two different types of wireless systems.
2. Background of the Present Invention
Wireless telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. The development of wireless telecommunications has evolved from analog radio frequency (RF) technology into digital RF technology. The main types of analog systems are: Advanced Mobile Phone System (AMPS), Nordic Mobile Telephone (NMT) and Total Access Communications System (TACS). Within the digital systems, the main types are as follows: Global System for Mobile Communications (GSM), Time-Division Multiple Access (TDMA), of which the Digital-AMPS (DAMPS) system is one kind, and Code-Division Multiple Access (CDMA).
In addition, there are two world standards for these types of technologies: American National Standards Institute (ANSI) for the United States and Canada, and Consultative Committee for International Telephone and Telegraph (CCIT) for virtually the rest of the world. The ANSI standards focus on the AMPS and D-AMPS technologies, while the CCIT standards focus on the NMT and GSM standards.
With all of these different types of wireless communications systems available, seamless roaming from one type of system to another has posed significant problems for the industry. For example, if a mobile subscriber is involved in a wireless call, and the call needs to be handed over to another type of system in order to continue the call, conversion and interface devices are needed to perform this task. One device that exists today to perform such handovers between D-AMPS and GSM systems is a Roam-Free Gateway (RFG), formerly known as an Interworking Location Register (ILR). The RFG acts as a gateway that converts the protocols of the signaling and voice communications between the systems to enable the two systems to communicate effectively in order to perform call handovers. However, the RFG device only works handovers between the D-AMPS and GSM systems. Other conversion and interface devices must be used for other types of systems. Implementing each of these devices has proved extremely difficult and costly for network providers.
The present invention is directed to telecommunications systems and methods for utilizing an Internet telephony system to perform a handover of a call between different types of wireless systems. When a serving mobile switching center (MSC) determines that there is not another MSC belonging to the same type of wireless system to which a handover can be performed, the serving MSC sends an identity message to an Internet Gatekeeper via an Internet Gateway for the serving MSC. This identity message inquires whether there are any other types of wireless systems nearby. The Internet Gatekeeper maintains a database of all existing wireless systems within the area served by the Internet Gatekeeper. The Internet Gatekeeper chooses a target MSC of another wireless system (if possible), and transmits the identity of this target MSC back to the currently serving MSC. Thereafter, the currently serving MSC performs the handover to the target MSC by routing signaling messages and voice or data communications through the Internet Gateways and the Internet Gatekeeper to the target MSC.